南海-西北太平洋季风槽中热带气旋群发的研究 Ⅰ.热带气旋群发的基本特征

应用1979—2005年西北太平洋热带气旋(TC)资料和NCEP/DOE AMIP-Ⅱ逐日再分析资料,在逐年分析南海-西北太平洋季风槽中TC(简称MTTC)生成及其群发的基础上,揭示季风槽中MTTC群发的基本特征,得到几点结论:(1)年平均MTTC群发过程3~4次,8月是MTTC群发最多的月份,占30%,9月次之,而5月份最少,仅占4%;(2)MTTC群发异常偏少年MTTC生成海区范围较常年偏小,位置较正常年份偏南、偏西;而异常偏多年MTTC生成海区范围较大,位置较常年偏北、偏东;(3)MTTC群发主要形成于4种季风槽环流模态中,即季风槽东伸型、反向季风槽型、三气流型、西太平洋季风槽型,其中,季风槽东伸型是MTTC群发的主要环流模态,占60.0%,西太平洋季风槽出现MTTC群发最少,仅占4.8%;(4)季风槽强度和形态的异常可能造成MTTC群发异常,而MTTC群发异常致使MTTC年频数异常。

Research on the cluster of tropical cyclogenesis in the South China Sea-western North Pacific monsoon trough I.Major features about the cluster of tropical cyclogenesis

By using the western North Pacific tropical cyclone(TC)data and the NCEP/DOE AMIP-Ⅱ reanalysis daily data during 1979-2005, the features of TCs in the South China Sea(SCS)-western North Pacific monsoon trough (MTTC) and the cluster of tropical cyclogensis (CTC) are analysed. The main results are shown as follows: (1)The average frequency of the CTC is 3~4 times per year. In August, the number of the CTC is maximum, occupying 30%, followed by September, and it is minimum in May, only accounting for 4%. (2) The MTTCs genesis area is smaller (bigger), located more south-(north-) and west-(eastward) than normal in inactive (active) years.(3)CTC mainly formed in four monsoon trough (MT) patterns: eastward extend MT, reverse-oriented MT, the three streams MT and western Pacific MT, of which the first pattern is the chief, in which 60.0% of MTTC form, the last one is the least, only accounting for 4.8%. (4) Anomalies in the intensity and pattern of monsoon trough lead to the abnormal CTCs which result in the abnormal frequency of MTTCs.